System for corrosion inhibition

ABSTRACT

AQUEOUS ACID SOLUTIONS ARE INHIBITED AGAINST CORROSION OF METALS, ESPECIALLY FERROUS METALS, BY INCORPORATION OF A CORROSION-INHIBITING SYSTEM COMPOSED OF A COMBINATION OF 1-HEXYN-3-OL, 5-DECYN-4,7-DIOL, AND 3-METHYL-1-BUTYN-O-O1.

United Sttes US. Cl. 252-146 7 Claims ABSTRACT OF THE DISCLOSURE Aqueous acid solutions are inhibited against corrosion of metals, especially ferrous metals, by incorporation of a corrosion-inhibiting system composed of a combination of 1-hexyn-3-ol, -decyn-4,7-diol, and 3-methyl-l-butyn-3-o1.

This invention relates to the inhibition of metal corrosion in acidic solutions and is more particularly concerned with inhibited aqueous acid solutions suitable for the treatment of metals.

Metal cleaning baths and pickling baths generally comprise aqueous solutions of inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid, and are useful in the cleaning and treatment of iron, zinc, ferrous alloys, and the like.

In the use of aqueous acidic baths to treat metals, additives or inhibitors in the baths are desirable to prevent or inhibit corrision or erosion of the metal surfaces. Similarly, in the field of oil-well acidizing, it is necessary to use inhibitors in order to prevent corrosion of the oilwell equipment by the aqueous acid solutions employed. Various other industrial operations also involve contact between an aqueous acidic solution and a metal, and an inhibitor must be used in order to minimize corrosion and/ or consumption of the metal by such contact.

If no corrosion inhibitor is present when the aqueous acidic solution comes into contact with the metal, excessive metal loss, production of undesirable metal surface properties, excessive consumption or loss of acid, and like adverse results will be experienced. Many different types of inhibitors have been proposed, but there has been a continuing search for corrosion inhibitors which can be used eflfectively in small concentrations, and which are economical to produce, since the use of inhibitors is a necessary expense and it is economically prudent to keep this expense at a minimum while, at the same time, realizing the desired inhibition of metallic corrosion or consumption. The need is also for corrosion inhibitors which are effective at high temperatures, e.g. 200 F. and above, such as are encountered in various operations involving acidic solutions, particularly oil-well acidizing where higher and higher temperatures are encountered as the well extends further into the earth.

While various corrosion-inhibiting agents have ben proposed, all of such agents are not of equal effectiveness and of the many hundreds of agents which have been contemplated, only a few are sufficiently active to be commercially attractive. This is particularly true in the case of high-temperature operations. Some inhibitors which have been proposed are reasonably effective at low and moderate temperatures, but fail completely when high temperatures are encountered.

There has, therefore, been a continuing search for more efiective inhibitors, or for ways of making a given inhibitor more effective. This search has involved the discovery of combinations of inhibitors which act together to provide an inhibitor system. However, many of these systems involve relatively expensive components so that, while they may be relatively effective in their corrosion-inhibiting activity, there are disadvantages from an economic ice standpoint, particularly if they have to be used in substantial quantities in order to bring about the desired corrosion-inhibiting activity. Similarly, many of these systems. are ineffective at elevated temperatures. In particular, there is a need for a corrosion-inhibiting system comprising a plurality of components wherein relatively inexpensive compounds of poor corrosion-inhibiting action can be catalyzed or potentiated by the other component or components of the system so that the combination has a high corrosion-inhibiting activity even at elevated temperatures.

It is accordingly an object of this invention to provide a novel corrosion-inhibiting system involving a combination of agents which is highly effective from the standpoint of corrosion-inhibiting activity and which is, at the same time, commercially attractive.

It is a further object of this invention to provide a novel corrosion-inhibiting system comprising a combination of agents wherein one agent has a strong potentiating or catalyzing action upon the other agent so that the corrosion-inhibiting effectiveness of the combination is greater than the additive action of the components of the combination.

It is another object of the invention to provide a corrosion-inhibiting system of the character indicated which is effective at high temperatures.

In accordance with this invention, it has been discovered that the above and other objects can be achieved by the provision of a corrosion-inhibiting system comprising a combination of l-hexyn-3-ol, 5-decyn-4,7-diol, and 3- methyl-lbutyn-3-ol. The ratios among the components of the corrosion-inhibiting system may vary, but the best results are obtained with weight ratios between the hexynol and the decyndiol ranging between 1:10 and 10:1, preferably l:5 and 5:1, and most suitably between 122 and 2:1, and with the weight ratios of the combined hexynol and decyndiol to the butynol ranging between 1:10 and 10: 1, preferably 1:5 and 5:1, and weight ratios between 1:2 and 2:1 being especially preferred.

The inhibitor system of this invention is useful in the inhibition of corrosion of metal surfaces in contact with aqueous mineral acid solutions, such as hydrochloric acid, sulfuric acid, and phosphoric acid, for example in the acidizing of oil wells, in electrolytic cleaning baths, and electrolytic refining of metals, as well as in metal cleaning and pickling baths. The use of the above-described inhibitor system of this invention for corrosion inhibition of metals in aqueous mineral acid solutions is advantageous in that this corrosion inhibitor system can be employed in such acid solutions over a wide and useful concentration range. A further advantage of this inhibitor system is that it may be used at elevated temperatures to provide satisfactory corrosion inhibition, even when in relatively low concentration.

The most effective amount of the corrosion-inhibiting system to be used in accordance with this invention can vary, depending upon local operation conditions. Thus, the temperature and other characteristics of the acid corrosive system may have a bearing upon the amount of inhibitor to be used. The higher the temperature and/or the higher the acid concentration, the greater is the amount of corrosion inhibitor required to give optimum results. In general, however, it has been found that a concentration of the corrosion-inhibiting system of the invention between 0.01 and 2%, preferably between 0.01% to 1.2%, by weight of the aqueous acidic solution is an effective corrosion-inhibiting concentration, although higher concentrations can be used when conditions make them desirable, with a concentraton between 0.05% to 0.75% by weight being of most general use, at elevated temperatures, e.g. in the neighborhood of 200 F. The acidic solution can be dilute or concentrated and can be of any of the concentrations used in treating metals, e.g. ferrous metals, or for operations involving contact of acidic solutions with such metals, e.g. oil-well acidizing, and the like, for example 5 to 80%. In most operations of the character indicated, acid concentrations of 1015% by weight are employed, and non-oxidizing inorganic acids are used. However, it is not intended to limit the invention to any specific use of acidic solutions or with respect to any specific metal or acid.

While the inhibitor system of this invention can be prepared from individual quantities of 1-hexyn-3-ol and 5- decyn-4,7-diol, a particularly advantageous source of these two chemicals is the reaction mixture obtained by the ethynylation of butyraldehyde with acetylene, using the well-known reaction wherein butyraldehyde and acetylene are reacted in the presence of a catalyst in an inert solvent medium, most commonly an ether, the reaction being carried out at various temperatures but which generally lie in the range of to 50 C. This reaction, which was originally proposed by Favorskii, and has been improved upon by several other workers, is welldescribed in the literature, and reference is made, for example, to the book Acetylenic Compounds by Thomas F. Rutledge (Reinhold Book Corp., 1968), especially pages 146 to 149, and to the footnotes referred to therein. In a typical operation the aldehyde and the acetylene are reacted in an acetal or an ether as the reaction medium at substantially atmosphere pressure at a temperature of 20 to 30 C., using solid KOH as catalyst in amounts which are substantially stoichiometric (usually slightly in excess) with respect to the aldehyde, the acetylene being in excess of the stoichiometric quantity. The thus-produced mixture of 1-hexyn-3-ol and S-decyn- 4,7-diol will vary in composition somewhat, depending upon the specific reaction conditions, but the ratio of lhexyn-B-ol to -decyn-4,7-diol usually lies within the range of 5:1 to 1:4, and most commonly is about 1:1 to 2:1. The inert reaction medium is readily separated by distillation, but minor amounts of the solvent, e.g. up to by weight or more, may be present and such presence does not interfere with the activity of the acetylenic hydroxy compounds. The mixture may also contain minor amounts of by-products produced by condensation, aldolization, or other reactions and are also unobjecitonable. Such by-products may range up to 10% by weight but are usually less than about 5% by weight.

It will be understood that a reaction mixture of the character indicated is particularly attractive from a commercial standpoint since purification of the product of the ethynylation reaction is not required, yet the important benefits of the combination of 1-hexyn-3-ol with 5- decyn-4,7-diol in the system of this invention are realized in the critical area of corrosion inhibition, i.e. high acid concentrations and high temperatures.

The following experiments will serve to illustrate the eifectiveness of the corrosion-inhibiting system of this invention under severe corrosion conditions encountered in practical application:

The method used to determine the inhibiting properties of the system of the invention employs test specimens or coupons. To prepare the coupons, they are wiped with acetone to remove any residual oils or grease, and pickled for one minute in 10% hydrochloric acid to eliminate any scale and surface film. After pickling, the coupons are dipped in sodium bicarbonate solution, rinsed well in tap water, rinsed in distilled water, and finally dried with acetone. The clean and dry specimens are then weighed to the nearest 0.1 mg. In carrying out the evaluation, hydrochloric acid of by weight concentration is used in order to duplicate oil-well acidizing conditions. The inhibitor system is added to 4 oz. test bottles, 100 ml. of the acid then added to each bottle; and the mixture shaken vigorously. The bottles are suspended in a constant-temperature bath consisting of a bell jar filled 4 with ethylene glycol and equipped with a stirrer. The temperature is regulated to maintain the samples at 200:2 F. The bottles are placed in the bath /2 hour before the test coupons are added to insure temperature equilibrium. The weighed coupons, in duplicate, are then supported on glass hooks in the test bottles and the bottles are covered with Watch glasses during the testing period of 16 hours. At the end of the testing period, the bottles are removed from the bath, the coupons Withdrawn, rinsed with water, sodium bicarbonate solution, distilled water, and dried in acetone, then weighed to measure weight loss. Corrosion-inhibiting properties are conveniently expressed as percent inhibition, using the following formula:

Percent inhibition wt. loss of blankwt. loss of test coupon wt. loss of blank X100 Percent inhibition Original wt. test couponwt. loss of test coupon original wt. test coupon EXAMPLE Using the test procedure described above, the inhibitor system of the invention was evaluated for its effectiveness in preventing corrosion of N-SO grade steel, using coupons cut from actual tubing of the type employed in the oil industry. The coupons are cut from 2 in. seamless tubing and represent a 72 section having an axial dimension of 1.343 in. and a transverse dimension of 1.343 in. N steel is relatively susceptible to acid corrosion and has the following typical analysis: 0.38% carbon, 1.32% manganese, 0.02% phosphorous, 0.023% sulfur, 0.18% molybdenum, the balance iron. Each test sample was prepared by adding equal weight parts of 3-methyl-1- butyn-3-ol and of a mixture comprising 1-hexyn-3-ol and 5-decyn-4,7-diol in a 2:1 weight ratio to the 15 hydrochloric acid, the total combined system, i.e. the combined 3-methyl-1-butyn-3-ol and hexynol-glycol mixture, being added in the amount of 0.5% by weight of the acid. Each sample was evaluated for corrosion inhibiting activity in contact with the N-80 metal coupon. At the same time, a blank test, using the same acid but without any inhibitor, was made. The following results were obtained:

Percent inhibition,

Inhibitor: 16 hrs. Hexynol+5 decyn-4,7-diol|-3-methyl-l-butyn- None 0 The foregoing tests were repeated except that in one case the weight ratio of the 3-rnethyl-l-butyn-3-ol to the hexynol-glycol mixture was 2:1 and in a second case it was 1:2. In both cases a percent inhibition of 99 was recorded.

These tests show the positive action of the combination of hexynol, 5-decyn-4,7-diol, and 3-methyl-1-butyn-3-ol in accordance with this invention, in inhibiting metal corrosion of commercial steel tubing in an acid solution of high concentration at an elevated temperature only slightly below the boiling point of water, over a prolonged period of time. The results shown in the foregoing test data are obtained when an ethynylation reaction mixture comprising 1-hexyn-3-ol and 5-decyn-4,7-diol of the type described above is employed in combination with the 3- methyl-l-butyn-3-ol.

It will be apparent that various changes and modifications may be made in the operations described in the foregoing without departing from the scope of the invention as defined in the appended claims. It is intended, therefore, that all matter contained in the above description of the invention shall be interpreted as illustrative only and not as limitative.

We claim:

1. A metal corrosion-inhibitor mixture for use with aqueous mineral acids consisting essentially of 1-hexyn-3- ol, 5-decyn-4,7-diol and S-methyl-l-butyn-S-ol, wherein the hexynol and decyndiol are present in relation to each other in the weight ratios of from 1:10 to 10:1 and the hexynol and decyndiol are present in combination in the weight ratios of 1:10 to 10:1 in relation to the butynol.

2. An inhibitor mixture as defined in claim 1 wherein the hexynol and the decyndiol are present in combination in the weight ratios of 1:2 to 2:1 in relation to the butynol.

3. An inhibitor mixture as defined in claim 1 wherein the source of the hexynol and decyndiol is the reaction product formed by the ethynylation of butyraldehyde with acetylene.

4. A corrosion inhibited mineral acid comprising an aqueous solution of the mineral acid and a small, effective amount of a corrosion-inhibiting mixture consisting essentially of 1-hexyn-3-ol, 5-decyn-4,7-diol and 3-methyl- 1-butyn-3-ol, wherein the hexynol and decyndiol are present in relation to each other in the weight ratios of from 1:10 to 10:1 and the hexynol and decyndiol are present in combination in the Weight ratios of 1:10 to 10:1 in relation to the butynol.

5. A corrosion-inhibited acid as defined in claim 4 6 wherein the corrosion-inhibiting mixture is present in the amount of 0.01% to 2% by weight.

6. An inhibited mineral acid as defined in claim 4 wherein the source of the hexynol and decyndiol is the reaction product formed by the ethynylation of butyraldehyde with acetylene.

7. An inhibited mineral acid as defined in claim 5 wherein the hexynol and the decyndiol are present in combination in the weight ratios of 1:2 to 2:1 in relation to the butynol.

References Cited UNITED STATES PATENTS 3,125,475 3/1964 Livingston et a1. 13441 X 3,231,507 1/1966 Beale et a1. 252-146 3,382,179 5/1968 Keeney et a1. 252148 3,428,566 2/1969 Herman et al 134--41 X OTHER REFERENCES Rutledge, T. F: Acetylenic Compounds, Rheinhold Book Corp., 1968, pp. 146-9.

LEON D. ROSDOL, Primary Examiner A. I RADY, Assistant Examiner U.S. Cl. X.R. 252-8.55 C, 396 

